Method of separating frit sealed parts of an electron tube



June 25. 1968 M. K. BROWN 3,390,033

METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Filed Aug.13, 1964 2 Sheets-Sheet 1 INVENTOR.

Mm? flew/M BY June 25. 1968 M. K. BROWN 3,390,033

METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Filed Aug.13, 1964 2 Sheets-Sheet 2 7/1 fig/J United States Patent 3,390,033METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Martin K.Brown, Lancaster, Pa., assignor to Radio Corporation of America, acorporation of Delaware Filed Aug. 13, 1964, Ser. No. 389,365 '7 Claims.(Cl. 156-24) ABSTRACT OF THE DISCLOSURE The frit-sealed panel and funnelparts of a cathode ray tube are thermally processed to produce a bendingstress in the frit seal which causes the seal to fracture. The thermalprocessing is performed cyclically by alternate heating and then coolingboth parts (eg by alternate applications of hot and then cold water tothe exterior surfaces only of both parts) to produce successive temperature diiferentials of opposite sense between the exterior andinterior surfaces.

This invention relates to a method of separating glass bulb parts of anelectron tube which are sealed together with a glass frit material.

One kind of cathode ray tube bulb includes a shallow bowllike glassfaceplate panel and a glass funnel memher. The sidewall of the panel isbutt sealed to the large end of the funnel with a glass frit material.Because of the relatively high cost of the panel and funnel parts, it isdesirable, in the case of a defective tube, that the parts be separatedso that they can be salvaged for re-use.

In one prior art salvage method, either the panel or funnel is heated sothat it expands outwardly relative to the other. Such differentialexpansion produces a shearing stress on the seal and causes the seal tofracture. In another prior art method, the entire bulb is heated bothinside and out to weaken the frit seal. The bulb is then pressurized toforce the two parts apart, thereby fracturing the seal. Such prior artmethods,while useful, result in an undesirable high percentage ofdamaged bulb parts, particularly in the case of rectangularly shapedcathode ray tubes.

It is an object of this invention to provide a novel and improved methodof separating frit sealed electron tube bulb parts such as those of acathode ray tube.

It is also an object of the invention to reduce the scrap occurring insalvaging frit-sealed cathode ray tubes.

In accordance with the invention, two parts of an electron tube bulbwhich are sealed together with a glass frit, are thermally processed tocreate a temperature differential between the interior and exteriorsurfaces there of. Such a temperature differential produces a bendingstress in the seal which causes the seal to fracture. The thermalprocessing is preferably performed cyclically such as by alternately andsubstantially uniformly heating and then immediately cooling theexterior surfaces so as to produce a back and forth bending fatigue inthe seal.

In the drawings:

FIG. 1 is a partial longitudinal section of a cathode ray tube on whichthe invention may be practiced;

. FIGS. 2 and 3 are enlarged sections of a portion of the tube of FIG. 1illustrating various steps of processing in accordance with theinvention;

FIG. 4 is a partial longitudinal section of the tube of FIG. 1 withparts broken away illustrating another step in the process according tothe invention; and

FIG. 5 is a graph illustrating temperature differentials produced inaccordance with the processing of FIG. 4.

In FIG. 1, a cathode ray tube includes a glass bulb comprising afaceplate panel 14 and a funnel member 16. The panel 14 includes asaucer-shaped faceplate 18 hav- 3,390,033 Patented June 25, 1968 ing ashort peripheral sidewall 20 extending therefrom. The funnel 16 includesa frusto-conical portion 22 having a cylindrical neck portion 24extending from the small end thereof. The open end of the panel sidewall20 and the large end of the funnel 16 are butt sealed together with aglass frit seal 26.

The tube 10 may be of the shadow mask type and include a mosaic phosphorscreen 28, a. multiapertured shadow mask electrode 30, and a plural beamelectron gun apparatus 32.

Various compositions of glass frit material may be used for making thefrit seal 26. For example, zinc-lead-borate devitrifiable frits such asthose described in US. Patent 2,889,952, issued June 9, 1959, to S. A.Claypoole have been widely used and are preferred because of theirdevitrifiable properties.

The frit seal 26 is made by applying a ring of frit (provided in asuspension of paste-like consistency) to the funnel 16 and allowing itto dry. The panel 14 is then set on top of the frit ring and theassembly heated to cause a fusion of the frit to both the panel andfunnel. The seal 26 normally includes an external bead 34, and aninternal bead 36 as shown in FIG. 2.

It has been found that best results in separating the panel 14 from thefunnel 16 are usually obtained by first removing the external bead 34 byan optional acid etch treatment. When a devitrifiable zinc-lead-boratefrit is used, a nitric acid etch as described in US. Patent 2,852,- 352,issued to R. Landron, Jr. on Sept. 16, 1958, has been foundsatisfactory.

When an acid etch treatment is employed, it may be performed asillustrated in FIG. 2. As there shown, a spray of acid 38 is directedonto the bead 34 from a suitable nozzle 40. A plurality of nozzles 40may be positioned around the periphery of the tube 10 to spray theentire length of the bead 34. Alternatively, the external bead 34 of theseal 26 may be submerged in an acid bath. Best results have beenobtained when the acid etch is such as to substantially completelyremove the bead 34, but with as little as possible undercutting of theseal 26. Such a removal is illustrated in FIG. 3 which shows that theresulting seal surface 42 is substantially a continuation of theexterior funnel surface 43. It has been found that if the seal 26 isexcessively undercut, e.g. greater than 20 percent of the seal distance,chipping of the bulb parts frequently occurs when the seal issubsequently fractured.

Following the acid etch removal of the external head 34 (if such step isused) a thermal processing of the panel 14 and the funnel 16 adjacent tothe seal 26 is performed, e.g., as illustrated in F268. 4 and 5.

To fracture the seal 26, both the exterior surface 43 of the funnel 16and the exterior surface 44 of the panel 14 in the region of the seal 26are simultaneously heated such as by application of hot water thereto.The water may be applied by sprays 46 from suitable nozzles 48 so as toflow over both the funnel surface 43 and the panel surface 44 asindicated by the numeral 49'. A plurality, e.g. six, of the nozzles 48may be employed and positioned around the entire periphery of thecathode ray tube bulb 10. When the exterior surfaces 43 and 44 areheated as illustrated in FIG. 4, the panel and funnel expand along theexterior surfaces 43 and 44 and produce a bending stress in the seal 26.Depending upon the particular structure and composition of the seal 26,fracture thereof may occur with only this initial bending. However, ithas been found that the incidence of damaged bulb parts is reduced ifthis initial heating of the bulb is insuflicient, by itself, to produceseal fracture. Instead, it is preferred that a cyclical type of thermalprocessing be employed wherein an alternate heating and then immediatelycooling of the bulb parts causes a fracture of the seal 26. Suchcyclical thermal processing produces a back and forth bending fatigue ofthe seal which causes it to fracture cleanly without damage to the bulbparts.

To cyclically process the bulb parts, the initial heating of theexterior surfaces 43 and 44 is ceased and a cooling thereof is thenimmediately employed. The cooling step may be performed in a mannersimilar to the heating step, viz., by application of water sprays 46from the nozzles 48. Such a simuitaneous cooling of the ex teriorsurfaces 43 and 44 produces a bending stress in the seal 26 which is ofthe opposite sense from that produced by the initial heating of thesurfaces. The cycles of alternate heating and cooling of the exteriorsurfaces 43 and 44 are continued until the seal 26 is fractured as aresult of the back and forth bending fatigue induced therein.

As shown by the single solid curve of FIG. 5, the exterior temperaturesof the two bulb parts 14 and 16 at points A and B are substantiallyequal at any given time. Thus, the exterior surfaces 43 and 44 aresubstantially uniformly heated and cooled by the water sprays 46.

FIG. illustrates a preferred heating and cooling schedule which has beensuccessfully used in separating frit sealed panel and funnel parts of arectangular inch cathode ray tube bulb. In the graph of FIG. 5,temperature readings are plotted along the ordinate and elapsed time ofthe cyclical thermal processing along the abscissa. The temperaturereadings are those as recorded by four thermocouples, A, B, C, and Dpositioned as shown in FIG. 4 on the exterior panel surface 44, theexterior funnel surface 43, the interior funnel surface 50, and theinterior panel surface 51, respectively.

As indicated on the graph of FIG. 5, hot water at a temperature of about52 C. is applied to both of the exterior surface 43 and 44 for a periodof three minutes. During this time the temperature of the exteriorsurfaces 44 and 43, as indicated by thermocouples A and B, rises rapidlyfrom room temperature to approximately 52 C. within one minute and thenlevels off at that temperature. At the same time, the temperature of theinterior funnel surface 50, as indicated by thermocouple C, althoughlagging behind that of the exterior funnel surface 43, rises to slightlyabove 50 C. The temperature of the interior panel surface 51, asindicated by thermocouple D, lags even further behind, rising toapproximately 45.

After this initial three minute spray with 52 C. hot water, a spray 46of 21 C. cold water from the nozzles 48 is flowed over both of exteriorsurfaces 43 and 44 for a period of approximately three minutes. Duringthis time the surface temperatures of the panel and funnel drop asindicated by their respective curves. Then after this three minute spraywith cold water, both of the exterior surfaces 43 and 44 are againheated with a 52 C. hot water spray 46, which causes the surfacetemperatures of the panel and funnel to again rise, this time as shownby their respective curves beyond the six minute mark on the graph.

In treating a 25" rectangular shadow mask bulb as described withreference to the graph of FIG. 5, a fracture of the frit seal 26 hasconsistently occurred after about 6 minutes of elapsed time. As shown bythe graph of FIG. 5, at the 6 /2 minute mark the exterior surfaces 43and 44 are at a substantially higher temperature than the interiorsurfaces 50 and 51. Such a temperature differential establishes that thefracture is occurring, not because of a lateral shear induced in theseal, but rather because of a bending fatigue as hereinbefore described.

For a given bulb-design and seal structure and composition, thetemperatures and durations of application of the heating and coolingmedia may be adjusted to produce seal fracture after two, three, or morecycles of thermal processing. While the three cycle (heat-cool-heat)process described with reference to FIG. 5 has been found preferable forone design of rectangular 25 inch bulb, a twocyclc process may besuccessfully used, and may, in fact, be preferred for some other bulbdesigns. Generally speaking, the more extreme the temperatures of theheating and cooling, the fewer the number of cycles that are required toproduce seal fracture. On the other hand, the less extreme thetemperatures, the greater the number of cycles required, and the lesslikely the chance of injury to the bulb parts.

Various thermal processing procedures to produce the desired temperaturedifferential between the exterior surfaces 43 and 44 and the interiorsurfaces 59 and 51 may be used. Instead of the preferred alternateheating and cooling of the exterior surfaccs43 and 44, a similaralternate heating and cooling may be applied to the interior surfaces 50and 51. Alternatively, the exterior surfaces 43 and 44 may be heated andthe interior surfaces 50 and 51 simultaneously cooled, this procedurebeing alternately reversed until seal fracture occurs.

Instead of the preferred spraying of hot and cold liquids onto only thefunnel 16 and allowing it to flow over both the funnel and panelsurfaces 43 and 44, the liquids may be sprayed onto only the panel 14and allowed to flow over both the funnel and panel surfaces 43 and 44.Alternatively, the spray itself may be directed onto both the panel 14and the funnel is.

Furthermore, thermal treatment by means other than liquid spray may beused. For example, hot and/or cold gases, e.g. air, may be directed ontothe panel and funnel surfaces. Also, the desired portions of the paneland funnel, i.e., those portions adjacent to the seal 26 may besubmerged in hot and/or cold liquid baths.

Any of these or other thermal processing procedures may be used providedthey are such as to produce the desired temperature differential betweenthe exterior surfaces 43 and 44 and the interior surfaces 50 and 51,whereby to produce the seal-fracturing bending stress. However, it hasbeen found through practice that best and speediest results are obtainedwhen the faceplate 18 is not directly heated during the thermalprocessing. For example, if water spray is used, the tube 10 is sopositioned and the spray so controlled as to minimize the how of waterover the faceplate.

The choice of means for performing the thermal processing may, to alarge degree, depend upon the type of cathode ray tube involved and thealready existing condition of the electrode parts therein. For example,in the case of a shadow mask cathode ray tube having a good shadow maskelectrode 30 therein, it is undesirable to introduce into the tube anyheating medium such as hot water which would be corrosive to the maskelectrode. In such a case, it is preferable to apply the thermalprocessing to only the exterior surfaces 43 and 44, or to use anon-corrosive treating medium such as dry air in thermally treating theinterior surfaces 59 and 51.

In separating cathode ray tube bulb parts as described above, anadditional optional step which may be used involves the application oflow air pressure to the inside of the bulb. As shown in FIG. 4, the neckof the tube it) may be closed with a stopper 52 and air pressure appliedto within the tube by a hose 54 connected between the stopper 52 and asource of compressed air 56. A pressure of about one lb. per sq. inch orless relative to the pressure on the exterior of the bulb is adequate.Such a pressure may be applied throughout all or any terminal part ofthe thermal processing of the bulb parts. For example, it may be appliedonly during the last thermal cycle before seal fracture. Applications oflow air pressure within the bulb: (l) aids in the separation of the bulbparts, (2) serves to indicate to the operator when seal fracture hasoccurred, and (3) prevents water from seeping into the bulb through theseal fracture and causing possible corrosive damage to the maskelectrode 3t).

What is claimed is:

l. The method of separatin two glass parts of an electron tube bulbsealed together with a glass frit seal, comprising the steps of:alternately and substantially uniformly heating and cooling the exteriorsurfaces only of both said parts adjacent to said seal in immediatesuccession to produce bending stress of alternating sense in said sealto thereby cause bending fatigue and fracture of said seal thetemperatures of both of said exterior surfaces being substantially thesame during said method.

2. The method of separating two glass electron tube bulb parts sealedtogether with a divitrified glass frit seal, comprising the steps of:

(a) acid etching a surface of said seal, and

(b) alternately and substantially uniformly heating and cooling theexterior surfaces only of both said parts adjacent to said seal inimmediate succession to produce a fracture of said seal the temperaturesof both of said exterior surfaces being substantially the same duringthe heating and cooling steps.

3. In the method of separating two glass parts of a cathode ray tubebulb which are butt sealed together with a glass frit and which haveexterior and interior surfaces, said method comprising the steps of:

(a) creating a temperature differential of one sense between saidexterior and interior surfaces of said parts adjacent to said seal, andthen immediately (b) creating a temperature differential of the oppositesense between said exterior and interior surfaces of said parts adjacentto said seal the temperatures of both of said exterior surfaces beingsubstantially the same during said method.

4. The method of separating a faceplate panel part from a funnel part ofa cathode ray tube bulb having exterior and interior surfaces, saidparts being butt sealed together by a seal of devitrifiedZinc-lead-borate glass frit, said seal having an external bead portionextending around said tube, said method comprising the steps of:

(a) acid etching the exterior surface of said seal to remove saidexternal bead therefrom, then (b) heating the exterior surfaces only ofboth said panel and said funnel in the region of said seal, thenimmediately (c) cooling the exterior surfaces only of both said paneland said funnel in the region of said seal, and then immediately ((1)heating the exterior surfaces only of both said panel and said funnel inthe region of said seal while applying low air pressure to within thebulb,

(e) whereby to produce successive temperature differentials ofalternating sense between said exterior and interior surfaces andthereby fracture said seal, the temperatures of both of said exteriorsurfaces being substantially the same during the heating and coolingsteps.

5. The method of separating a faceplate panel part from a funnel part ofa cathode ray tube bulb, which parts are butt sealed together by a fritseal and which have an exterior and an interior surface, said methodcomprising the steps of (a) flowing hot water over said exteriorsurfaces only of said panel and said funnel in the region of said seal,then immediately (b) flowing cold water over said exterior surfaces onlyof said panel and said funnel in the region of said seal, and thenimmediately (c) flowing hot water over said exterior surfaces only ofsaid panel and said funnel in the region of said seal, the temperaturesof both of said exterior surfaces being substantially the same duringsaid method.

6. The method of separating two glass parts of a cathode ray tube bulbwhich has an exterior and an interior surface, said parts being buttsealed together with a glass frit seal, said method comprising the stepsof acid etching the exterior surface of said seal, and then in immediatesuccession successively heating then cooling, then heating the exteriorsurfaces only of both of said parts adjacent to said seal by alternatehot and cold water sprays, whereby temperature differentials ofalternating sense are successively created in said parts between theexterior and interior surfaces thereof which produce bending fatiguewithin and fracture of said seal, the temperatures of both of saidexterior surfaces being substantially the same during the heating andcooling steps.

7. The method of separating two glass parts of a cathode ray tube bulbwhich has an exterior and an interior surface, said parts being buttsealed together with a glass frit seal, said method comprising the stepsof:

(a) acid etching the exterior surface of said seal; and

then

(b) alternately and substantially uniformly heating and cooling theexterior surfaces of both of said parts adjacent to said seal to producesuccessive temperature differentials of alternating sense between theexterior and interior surfaces of said parts, and

(c) applying low air pressure to within said bulb during at least aportion of said heating and cooling steps and maintaining said pressureuntil said seal fractures, the temperatures of both of said exteriorsurfaces being substantially the same during the heating and coolingsteps.

References Cited UNITED STATES PATENTS JACOB H. STEINBERG, PrimaryExaminer.

